1. Field of the Invention
The present invention relates to an automated storage library having the inventory of its contents at the picker level. More particularly, the present invention is an automated storage library having a plurality of library controllers and pickers with the library inventory maintained in the picker controllers to permit any library controller to access any storage medium in the library without knowledge of the storage cell or drive in the library in which the storage medium resides.
2. Description of the Related Art
The main components of a computer system includes host processors, input/output (I/O) devices, and storage. Processors are the brain of computer systems, performing arithmetic and logical operations. I/O devices permit data to be input to or output from the system. A keyboard is an example of an input device and a printer is an example of an output device. Storage includes means for temporarily and permanently storing information, including user data and the instructions which direct computer operations. Storage may be within a processor, such as an integrated circuit main memory, or may be peripheral thereto, such as magnetic disks, magnetic tapes, and optical disks. A machine used to write to and read from such peripheral storage is known as a peripheral storage device and typically includes a device controller for translating processor commands into the physical actions of the device itself. Each of the computer system components may be divided into subcomponents and may be distributed across various locations within the computer system.
It is inefficient to store all of the data in a computer system on a single type of storage. Storing all data in main memory is too costly and storing all data on peripheral storage reduces performance. Thus, a typical computer system includes both main memory and one or more types of peripheral storage arranged in a data storage hierarchy. As the need for storage has increased, automated storage libraries have been developed to manage the storage of removable data storage media.
Automated storage libraries include a plurality of storage cells for retaining disks, tapes, or the like, a robotic picker mechanism, and one or more internal peripheral storage devices. Each storage medium may be contained in a cassette or cartridge for easier handling by the picker. The picker operates on command to transfer the storage media between the storage cells and internal peripheral storage devices without manual assistance. Once a storage medium is mounted in a peripheral storage device, data may be written to or read from that medium for as long as the system so requires.
Several automated storage libraries are shown. IBM Corporation introduced the 3850 Mass Storage Subsystem for the storage and retrieval of magnetic tape modules in the 1970's. More recently, several firms have introduced automated storage libraries for magnetic tape cartridges and optical disk cartridges. For example, magnetic tape cartridge libraries are disclosed in U.S. Pat. Nos. 4,654,727, 4,864,438, and 4,864,511. Examples of optical disk libraries can be found in U.S. Pat. Nos. 4,271,489, 4,527,262, 4,614,474, and 4,766,581. These libraries are designed to attach to a computer system in which a host processor maintains an inventory of the location of each storage media therein. To access a file of data in the library, the host processor must first identify the storage medium upon which the file is stored and then determine the storage cell or internal peripheral storage device in which such storage medium resides. The host processor then commands the appropriate picker controller and/or peripheral storage device controller to access the file. Should a failure cause the loss the storage media inventory, a new inventory is generated by transferring each storage medium to a peripheral storage device for its identification. In the alternative, some libraries include a vision system on a picker which allows the inventory to be generated without transferring each storage medium to a peripheral storage device. Instead, the vision system is used to identify each storage medium while it resides in a storage cell.
Commonly assigned U.S. Pat. No. 5,121,483, hereby incorporated by reference, discloses an automated storage library in which the storage media inventory is maintained in a system or library controller, similar to that in a host processor. Upon receipt of a request for access to a storage medium in the library, the library controller uses its inventory to locate the storage medium. The library controller then directs the appropriate picker controller and/or peripheral storage device controller, as required. Should a failure cause the library controller to lose its inventory, a new inventory must again be generated.
Commonly assigned U.S. Pat. No. 5,289,589, hereby incorporated by reference, discloses an automated storage library with various redundancies to improve data accessibility. The library includes two library controllers and four pickers. Each library controller maintains a storage media inventory for the entire library. Each picker has exclusive access to a set of storage cells and internal peripheral storage devices. Normally, one library controller directs the operation of two pickers and the other library controller directs the operation of the other two pickers, but each library controller is coupled to each picker. The library controllers are also coupled to each other such that both of their storage media inventories are updated as storage media and transferred about the library, regardless of the picker(s) used for the transfer operations. During a failure condition which prevents one library controller from accessing a particular storage medium, the other library controller can be signalled to attempt to access such storage medium. This is possible because both library controllers have the required storage media inventory. Should a single library controller lose its inventory, such inventory can be generated simply by accessing the inventory in the other library controller. Unfortunately, the time required to maintain two identical copies of the storage media inventory for the entire library is overhead which degrades library performance. Furthermore, such overhead increases as the activity in the library increases.